Fire alarm systems are often installed within commercial, residential, educational, or governmental buildings, to list a few examples. These fire alarm systems typically include control panels and fire detection devices, which monitor the buildings for indicators of fire. In one example, the fire detection devices are individually addressable smoke detectors that are part of a network. The detectors send event data to the control panel, which analyzes the received event data. In more detail, the smoke causes a change at the detector, such as an increase in a scatter light signal, which is sent to the panel as an event and which after processing by the panel will cause an alarm if the smoke exceeds a preprogrammed threshold.
In another example, the fire alarm system is comprised of standalone or independent fire detection devices. This type of system is often implemented in residential buildings where there is a smaller area to monitor and building code requirements are more relaxed. While each device operates independently from the other devices of the system, the devices are often interconnected such that if one device is activated into an alarm state, then all of the devices enter the alarm state.
Two common types of fire detection devices are photoelectric (or optical) smoke detectors and ionization smoke detectors. The optical smoke detectors often include a baffle system, which defines a detection chamber, to block ambient light while also allowing air to flow into the detection chamber. The optical smoke detectors further include a smoke detection system within the detection chamber for detecting the presence of smoke. The smoke detection system typically comprises a chamber light source and a scattered light photodetector. When smoke fills the detection chamber it causes the light from the chamber light source to be scattered within the chamber and detected by the scattered light photodetector. Ionization smoke detectors also typically have a detection chamber containing an ionizing radioisotope. When smoke fills the detection chamber, the electronics of the smoke detector detect a change in a current arising from the ionization of the smoke. While ionization smoke detectors also include a baffle system to protect the detection chamber, the baffle system it is typically designed to prevent moisture from entering the detection chamber because it can affect the accuracy of the smoke detector.
Currently, building codes often require that the smoke detectors be tested annually. This annual testing is performed because smoke detectors have a number of different failure points. For example, the electronics or optics of the device can fail. Likewise, the detectors can become so dirty that the baffle systems become clogged. Additionally, it is not uncommon for the smoke detectors to get painted over or for insects or spiders to build nests or webs in the detectors.
The annual testing of the devices is commonly performed by a technician performing a walkthrough test. The technician walks through the building and manually tests each of the fire detection devices of the fire alarm system. In the case of smoke detectors, the technician often uses a special testing device. In one example. The testing device includes an artificial smoke generating apparatus housed within a hood at the end of a pole. The technician places the hood around the fire detection device and the artificial smoke generating device releases artificial smoke near the detector. If the smoke detector is functioning properly, it will trigger in response to the smoke. The technician repeats this process for every smoke detector of the fire alarm system.
On the other hand, self-testing fire detection devices have been proposed. In one specific example, a self-test circuit for a smoke detector periodically tests whether the sensitivity of a scattered light photodetector is within a predetermined range of acceptable sensitivities. If the sensitivity of the scattered light photodetector is out of the predetermined range of acceptable sensitivities, then a fault indication is produced.